Where do we get most of our information and understanding about the world beyond Britain - particularly those far-flung developing countries you can't reach for £50 and a ham sandwich on Ryanair?

For most people, the answer is still television. Through news bulletins, documentaries and factual programmes - whether they are about or just located in other countries - British viewers can be exposed to different cultures, landscapes and ethnic groups. At a time when virtually every aspect of our lives has become more global - from the food we eat to our holidays and concerns about immigration and national security - an international perspective is more important than ever.

It is therefore disappointing to find that, despite the events in Iraq, Afghanistan and elsewhere, factual programming about developing countries is at its lowest recorded level. The Third World and Environment Broadcasting Project (3WE) has been tracking the coverage of developing countries on British terrestrial television since 1989. The latest analysis, which we carried out for 3WE at the University of Westminster, shows there were 197 hours of terrestrial coverage last year, 49% down on 15 years ago - even including additional hours from Five. For digital viewers there were an extra 61 hours on BBC3 and BBC4.

The two mainstream channels were the worst offenders, with BBC1 down 49% on 2000-01 to 20 hours, and ITV down 71% to 14 hours. Channel 4 came out top with just over 70 hours, despite a decline of more than 25%. Combined output from the two main BBC channels was down from 109 hours to 82, but this was more than compensated for by BBC4's 61 hours. The BBC might therefore claim it is still fulfilling its role in international programming, but this suggests some migration from terrestrial to digital channels.

There is better news in the breakdown of subject matter, with a greater emphasis on "harder" themes of conflict and disaster. Programmes such as Fighting the War on BBC2 and Battle Stations Iraq on Channel 4 made up 20% of all developing country output, compared with 2% in 2000-01. More than half of these programmes - 32 out of 55 - went out on Channel 4, with another 18 on BBC2. History also featured more heavily, with 54 programmes compared with 31 in 2000-01.

The amount of all international factual programming - on developed as well as developing countries - has remained fairly stable over 15 years. The addition of Five and the BBC's digital channels took the total to just over 913 hours last year, below the 2000-01 total. A striking finding is the growing dominance of foreign travel themes, with shows such as BBC1's Passport to the Sun and ITV's Wish You Were Here ... ? Today. It is arguable whether these programmes and others which feature Britons settling abroad (Get A New Life, for example) contribute to a better understanding of different cultures, but the local emphasis means they are likely to become more frequent.

Broadcasters like to claim that news programmes today feature the same kind of analysis as longer factual programmes. This is debatable, given that news items cannot match the length and depth of a dedicated programme. But the importance of news bulletins in delivering large audiences means foreign news content is at least as crucial as dedicated shows. Our analysis of news for last year shows a continuing commitment to international coverage, especially from Channel 4 and the BBC's late evening bulletin.

Traditionally, both ITV and BBC have left foreign news to the late bulletins and given a more domestic emphasis in the early evening. This trend has accelerated at the BBC, which last year devoted 50% of its late news content to foreign items. This is in contrast to ITV's late bulletin, which last year devoted only 32% to foreign news. Despite the war in Iraq, ITV's foreign coverage on its late news was little more than in 1999.

After 40 years of competitive editorial approaches, it now looks as though the BBC's late evening editorial policy is becoming distinct from ITV's. Channel 4 News, meanwhile, has been astonishingly consistent, maintaining a 40% level of foreign news for the past 20 years.

Within foreign news, stories about developing countries dominated all bulletins during 2003, driven by events in Iraq. Before that, however, there was evidence of a progressive decline in third world coverage in the years to 1995, with a slight increase in 1999. It is not clear whether there have been conscious editorial decisions to reduce the emphasis, but all bulletins have been remarkably similar over the years in the way their foreign coverage is distributed among the regions of the world.

International programming has always been accepted as an integral part of the public service broadcasting tradition, and is explicitly mentioned in the Communications Act. As terrestrial television becomes more competitive and the immediate crisis in Iraq recedes, the difficult question for the regulator Ofcom will be how to define "international" and what level of commitment to demand from the commercial sector.

It will be tempting for commercial broadcasters in particular to argue that reality shows based in exotic locations should qualify as their contribution, while the "serious" stuff is left to the BBC. When this research is repeated in two years' time, we are unlikely to find mainstream television channels making a greater contribution to understanding the world outside Britain.

· Steven Barnett is a professor of communications at the University of Westminster. The World on the Box by Caroline Dover and Steven Barnett is published today and is available on www.epolitix.com/forum/3WE or for £5 incl p&p from International Broadcasting Trust (020-7874 7650)